Catheters comprise tube-like members that are inserted into the body for various medical reasons, some diagnostic and others therapeutic. While in many instances the steerability or directionality of such catheters is of concern, steerability is particularly important with regard to certain urological or cardiovascular applications.
There have been various attempts to develop steerable catheters. For example, U.S. Pat. No. 1,060,665 describes an early attempt to provide a catheter capable of some direction. However, the device disclosed in this patent, as well as catheters and catheter guides disclosed in later patents, such as U.S. Pat. Nos. 2,574,840 and 2,688,329, tend to be characterized by only limited directionality.
In addition, some supposedly steerable catheters are too large and rigid to be of practical use in cardiovascular techniques. See, for example, U.S. Pat. Nos. 3,470,876 and 3,605,725, where wires equidistantly positioned along the length of a catheter are connected to a steering means which pulls on the wires to cause the distal end of the catheter to go in a desired direction. Moreover, U.S. Pat. Nos. 3,521,620, 3,547,103, 3,625,200, and 4,020,829 describe coil spring guide wires that have a certain degree of directionality but are too rigid for safe usage in certain delicate cardiovascular procedures.
According to U.S. Pat. No. 4,033,331, a coronary catheter has a main lumen and a shaping wire lumen. When the wire is withdrawn through the shaping wire lumen, the catheter assumes certain predetermined configurations. While this so-called steerable catheter is useful in some cardiovascular applications, such as positioning the initial guiding catheter guide through which other devices are guided, its limited directionality and limited tip control preclude extensive use.
A medical procedure known as percutaneous transluminal coronary angioplasty (PTCA) was developed in approximately 1976-1977 by Dr. Andreas Gruntzig. According to this procedure, blockage in a coronary artery can be reduced by positioning a balloon dilatation catheter across the blockage and then inflating the balloon, which causes the blockage to decrease. Such positioning requires that the balloon dilatation catheter be "steered" into place, that is, across the stenotic lesion causing the blockage, by manipulation at the proximal end of the catheter.
The procedure is actually somewhat complex, consisting of introducing a catheter system via the femoral or brachial artery under local anesthesia. A pre-shaped guiding catheter is positioned into the orifice of the coronary artery, and through this guiding catheter a second, dilatation catheter is advanced into the branches of the coronary artery. The dilatation catheter has an elliptically shaped balloon portion near the tip which can be inflated and deflated. After traversal of the stenotic lesion of the coronary artery, the balloon portion is inflated with fluid, which dilates the lumen of the vessel.
The PTCA procedure and equipment have become increasingly refined over the past seven years. The first marketable PTCA apparatus consisted of a small catheter with a single balloon port and no central lumen, that is, a so-called "fixed wire" system, which terminated in lateral openings at the distal end thereof. This system, which is the subject of U.S. Pat. No. 4,195,637, was designed by Dr. Gruntzig and was marketed in the United States by USCI. The fixed wire catheter system disclosed in U.S. Pat. No. 4,195,637 comprises a balloon dilatation catheter and a low friction guide catheter consisting of one tubular member fitted into a more rigid, shrunk-on tubular member that is not co-extensive. The distal end of the balloon dilatation catheter has a flexible tip advantageously fabricated from a spring steel wire.
In 1980-1981, Dr. John Simpson, working at Stanford University, began to modify the fixed wire system and eventually developed a catheter with a free central lumen for movable guide wires and with a dilatation balloon formed from the outer surface covering in a unitary, that is, one-piece, construction. This catheter system is the subject of U.S. Pat. No. 4,323,071, which is assigned to Advanced Cardiovascular Systems, Inc. (ACS), formerly known as Advanced Catheter Systems, Inc. By use of such a movable wire system, one could more readily select the desired coronary artery and get to smaller branches since the movable guide wires are inherently smaller and more flexible than the fixed wire system. Subsequent to the development of the catheter with movable guide wires, known as the Simpson-Robert system and marketed by ACS, USCI has abandoned the fixed wire system and has marketed a similar device, calling it the steerable catheter, DILACA.RTM..
Samson, U.S. Pat. No. 4,516,972 issued May 14, 1985, to ACS. This patent is directed to a guide catheter having a helically wound ribbon of flexible material embedded in the wall of the catheter to provide torsional rigidity.
There is a further catheter system in use known as the Hartzler low profile catheter system, which is the subject of U.S. Pat. No. 4,582,181. According to this catheter system a balloon dilatation catheter has a concentrically contained guide wire extending the length of said catheter. Moreover, the distal end of the guide wire extends a short distance beyond the distal end of the balloon dilatation catheter and is affixed to the distal end of the balloon dilatation catheter.
The catheter system with movable guide wires and the low profile catheter system each represent an advance but still have disadvantages such as limited steerability, which is at present dependent upon the torquability, or torque control, of the movable wire. Steerability is highly significant in a cardiovascular procedure such as PTCA, or angioplasty, because less steerability results in greater time spent in the body and more possible patent trauma. Multiple insertions of guide wires and catheters can lead to thrombosis in that coagulation may commence along a guide wire surface and be forced into the heart when a catheter is slid over the guide wire. Furthermore, there are some blockages which simply can not be reached with presently known equipment.
There is definitely a need for more steerable catheter means, especially means useful n a procedure such as PTCA. Preferably such catheter means should have the following characteristics:
1. The catheter means may have an outer catheter shaft and an inner catheter to prevent bending of the inner catheter shaft, thus allowing more precise tip control.
2. The entire catheter (outer and inner) must be small enough to compare favorably with already existing small dilatation catheters.
3. The catheter should be capable of rotational and deflective movement. Rotational movement of the steering tip should be precise enough to provide as close to 1:1 torque as possible. This would make the device very useful since it could ultimately be substituted for high torque wires already available.
4. The inner catheter must be free enough to rotate inside the outer catheter so that the tip may turn freely in case another turning axis is needed (superior/inferior vs. lateral).
5. The steering catheter means should optionally have a balloon inflation port, if the catheter's o.d. is small enough to be competitive with the standard dilatation catheters. If this is the case, the space between the inner and outer catheters could be used as an inflation port.